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Chapter 8: Oxygen Demand. It is a measure of the amount of “reduced” organic and inorganic matter in a water Relates to oxygen consumption in a river or lake as a result of a pollution discharge Measured in several ways BOD - Biochemical Oxygen Demand COD - Chemical Oxygen Demand

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chapter 8 oxygen demand
Chapter 8: Oxygen Demand
  • It is a measure of the amount of “reduced” organic and inorganic matter in a water
  • Relates to oxygen consumption in a river or lake as a result of a pollution discharge
  • Measured in several ways
    • BOD - Biochemical Oxygen Demand
    • COD - Chemical Oxygen Demand
    • ThOD - Theoretical Oxygen Demand
theoretical oxygen demand
Theoretical Oxygen Demand

C6H12O6 + 6O2 = 6CO2 + 6H2O

Oxygen Demand

6moles*32g/mole Oxygen/1mole*180g/mole

= 1.06 O2 / Glucose

If glucose concentration is 360 mg/L THOD is

1.06 * 360 mg/L = 384 mg/L Oxygen

bod a bioassay
BOD: A Bioassay

Briefly, the BOD test employs a bacterial seed to catalyze the oxidation of 300 mL of full-strength or diluted wastewater. The strength of the un-diluted wastewater is then determined from the dilution factor and the difference between the initial D.O. and the final D.O.

BOD

Bottle

bod with dilution
BOD with Dilution

When BOD>8mg/L

  • Where
    • BODt = biochemical oxygen demand at t days, [mg/L]
    • DOi = initial dissolved oxygen in the sample bottle, [mg/L]
    • DOf = final dissolved oxygen in the sample bottle, [mg/L]
    • Vb = sample bottle volume, usually 300 or 250 mL, [mL]
    • Vs = sample volume, [mL]
bod loss of biodegradable organic matter oxygen demand

BOD

Bottle

BOD

Bottle

BOD

Bottle

BOD

Bottle

BOD

Bottle

BOD - loss of biodegradable organic matter (oxygen demand)

Lo

Lo-Lt = BODt

Lt

L or BOD remaining

Time

slide6
BOD

L=oxidizable carbonaceous material remaining to be oxidized

bod modeling
BOD Modeling

"L" is modelled as a simple 1st order decay:

Which leads to:

And combining with:

We get:

nbod nitrogeneous bod nbod
NBOD Nitrogeneous BOD (NBOD)

2 moles oxygen/1 mole of ammonia

4.57 grams oxygen/gram ammonia-nitrogen

Inorganic NH3, NO3- NO2-

Organic Proteins, Amino acids

TKN = Ammonia-N + Organic Nitrogen

cod a chemical test
COD: A chemical test

The chemical oxygen demand (COD) of a waste is measured in terms of the amount of potassium dichromate (K2Cr2O7) reduced by the sample during 2 hr of reflux in a medium of boiling, 50% H2SO4 and in the presence of a Ag2SO4 catalyst.

solids significance
Solids: significance
  • TDS: used as a measure of inorganic salt content in drinking waters and natural waters
  • TSS: used to assess clarifier performance
  • VSS: used to estimate bacterial populations in wastewater treatment systems
filtration for solids analysis

2. Pour

Sample

1. Weigh new

filter and insert

5. Measure

Change in

Weight

3. Start

suction pump

4. Remove filter

and re-weigh

Suction Flask & Filter Holder

Filtration for Solids Analysis

6. Divide this by the

Volume filtered and you get TSS